Automatic program selector



Feb. a 1945. PumNeTN 2,368,778

AUTOMATIC PROGRAM SELECTOR 5 Sheets-Sheet 1 Filed June 16, l942 KMFMS. m0

TON.

INVENTOR ELLlsON S. URING BY ,:4

ATTORNEY FMuoZou Feb. 6,1945.

RADIO TUNER E. S. PURINGTON AUTOMATIC PROGRAM SELECTOR Filed June lG, 1942 5 Sheets-Sheet 2 ELLISON S. PURINGTON.

b- 1 E. S.VPUR'INGTON 2,368,773

AUTOMATIC PROGRAM SELECTOR Filed June 16, 1942 5 Sheets-Sheet 3 32g 8 I Emu as q, 522 3 n a b- I a Egg 95% 'o.tb b tw F (3 12" m lm INVENTOR 2 ELUSON s. URINGTON.

BY W ATTORNEY Filed June 16, 1942 5 Sheets-Sheet 5 M T G T 4 N R U W w ms N 0 MY 8 F.

Patented Feb. s, 1945 AUTOMATIC PROGRAM SELECTOR Ellison S. Purlngton, Gloucester, Masa, assignor, by mesne assignments, to Radio Corporation of America, New Delaware York, N. Y., a corporation of Application June 16, 1942, Serial No. 447,215

I 1-1 Claims.

This invention relates to communication systems and more particularly to a systemfor automatically selecting a'desired type of program.

In general the invention relates to an automatic program selector used in connection witha receiver in which manually operated means are provided which condition the automatic program selector mechanism so as to be responsive to a predetermined transmitted signal indicative of the type of program to be transmitted.

The inventionis an improvement over the system disclosed and claimed in Hammond Patent No. 2,052,708 which is assigned to the same assignee as this application.

In the present invention the classification of programs may be, for example, concert, dance, variety, plays, quiz, news and sports. Each of these types Of programs is distinguished in the transmission by a definite sub-audible frequency. When the carrier is modulated by a concert program, it will be, for example, modulated also at a sub-audible rate of 21 cycles, for identification of the type of program bya receiver mechanism. For a dance program, the accompanyingfre quency would be, for example, 24 cycles, et cetera.

In general the lower designating frequencies are assigned to those types of. programs for which low audible frequencies are desirable- These signals are produced by a push button type oscillator, located in the studio and are injected into the studio amplifier at a suitable level,

for example, in place of a high level sound source such as phonograph pickup. This signal is mixed with the program which it identifies, with the sub-audible frequency, for example, at a level of -20 to 25 db. with respect to the program.

The receiver comprises a radio tuner of the pretuned type with a rotary motor driven scanner which tunes in each station participating in succession. During operation there will be produced in the audio portion of the receiver program energy of audible frequency and possible control energy of sub-audible frequency. The program energy is fed to an audio amplifier and the possible control energy to a control circuit,

which has a set of push buttons similarly marked to those at the transmitter. These set up the operating conditions of the control circuit so that its output will be energized only if the transmitter push button of the station being received is set to the same type of program as the push button of thereceiver. .With energization of the control circuit output a relay included therein is op- .erated to stop "the scanning motor thereby causing the motor-actuated radiotuner to be tuned to a broadcasting station transmitting the preselected type of program.

If a particular type of program happens to be transmitted by more than one broadcasting station at a given time, the station first to be received by the tuner during its scanning operation will be the one towhich the receiver will be tuned. In other words, if the operating carrier frequency of two stations transmitting the same type of program are 770 and 880 kilocycles and the previous setting of the tuner happened to be at, say, 660 kc., then the station operating at 770 kc. will be the one to be tuned in, assumingthat the tuning range of the receiver is scanned in the direction of higher frequencies. However, if scanning occurs in the direction of lower frequencies, the received station will be that operating at 880 kc.

If a broadcast station is tuned in by the motoractuated radio tuner and the program is not of the desired and preselected type, the relay in the control-circuit output will not operate and the motor will continue to tune in other broadcast stations until one transmitting the desired and preselected type of program is found. If after a sufficient lapse of time it becomes evident to-the receiver-operator that no broadcasting station is transmitting the desired type of program, he may choose topush a. button to preselect a different type of program. r

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended here to, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood.

system showing the interconnection of the several component parts represented in Figures 2 to5.

Like reference characters denote like parts in the several figures of the drawings.

In the following description and in the claims parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit."

Referring to the accompanying drawings and more particularly to Figure 1 the transmitter is shown as comprising a studio amplifier ii, a pro-' gram microphone i2 and a program identifying circuit l3, which includes a selector IS, an oscillator l8, s. buffer-amplifier [1, a filter l3 and an oscilloscope IS.

The selector It comprises two sets of resistors 2I--2I and 3l-3'|, each set being connected in series and to the contact points of a multiple push-button switch shown schematically at 33. Corresponding switch contact points have associated therewith one of a plurality of bridge contacts 39 which are operated selectively by a plurality of push buttons "-41 in a well known manner, so that when a push button is depressed the corresponding contact 33 will engage the corresponding points of the resistor assemblies. In the position shown the push button H for "plays" has been depressed moving the corresponding bridge contact 33 into engagement with the contact points of the resistors 24 and 34. The resistors 22, 24, 21, 32, 34 and 31 are vshown as adjustable for the purposes of adjusting the sub-audible frequencies.

The oscillator I3 is of the resistance-capacitance phase inverting type withthree capacitors 43, 49 and 50 and the two resistor assemblies 21-21 and 3l--3'| forming a resistance-capacitance low pass filter, which feeds energy from the plate to the grid of the oscillator tube 5|. The buffer-amplifier II includes an amplifier tube 32 which is connected in parallel with the grid of the oscillator tube 5|. The filter I8 is a resistor-capacitor band pass network which is program it identifies, with the sub-audible frequency, for example, at a level of to decibels with respect to the program.

The sub-audible frequencies can be checked against the frequency of the 60 cycle source 8! by means of the oscilloscope It. The oscilloscope I! can be used to check the frequencies 24, and 36 cycles and adjustments can be made by varying the resistors 22-32, 2H4 and 21--3I respectively. With the system set up accurately the adjustment of the resistors 21 and 31 for the 36 cycles will take care of the adjustments connected to the mixing circuits of the studio amplifier II. The amplifier i1 is also connected to a pair of opposite plates of the oscilloscope II the other plates of which are connected to a source of 60 cycle current 33.

Operation of Figure 1 In the operation of the transmitter shown in Figure 1 the oscillator i3 is of the resistancecapacitance phase inverting type which feeds energy from the plate to the grid of the tube M, which oscillates at a frequency for-which the grid is substantially out of phasewith the plate voltage. Because of the low pass functioning of the feed back circuit the output is relatively free from harmonics. The frequencies set up by the selector I! are so arranged that a lower frequency is secured by increasing the resistance in the circuit between both sets of filter condensers 43-50. When the contact 33 engages the contact points of the resistors 2| and 3| a frequency of 21 cycles is produced. When the contact 33 engages the contact points of the resistors 22-42, 23-43,. 24-34, 23-35, 23-38 and 21-31 frequencies of 24. 27, 30, 33, 36 and 39 cycles respectively will be produced.

The output of the oscillator 18 is amplified by the amplifier i1 and is further freed from harmonics in the audio frequency band by passing through the band pass filter i3.' The subaudible frequency is then injected into the mixing circuits in the studio amplifier ii at a suitable level where the signal is mixed with the for the 33 and 39 cycles, the adjustment of the resistors 23 and 34 for the 30 cycles will then take care of the adjustment for the 27 cycles and the adjustment of the resistors 22 and 32 -for the 24 cycles will take care of the adjustment for the 21 cycles.

It is contemplated that the push button identifying the signal will be set atthe beginning of each period allotted for a program and will run throughout its operation. This is to permit a receiver to pick up a program while in progress. It is understood, however, that it is within the scope of the present invention that the transmitter and receiver can be so arranged that the control system will be operative only during the first few minutes of each broadcast period after which the receiver will be held on that particu-- lar station until the end of the period. In Figure 1 push button H for plays" is shown as being depressed. Under these conditions 9. sub-audible frequency of 30 cycles will be produced by the oscillator I6 and will be injected into the studio amplifier il where it is mixed with the program.

Figure 2 depicts the receiver tuner and scanner and comprises a motor driven scanner 55, a radio tuner 58, 'a first detector or frequency converter 51 having associated with it a local oscillator circult 58, an intermediate frequency amplifier stage 59, a second detector and automatic volume control 60 and an audio and sub-audio frequency 1 preamplifier 6 I having an extended hub L2.

The scanner 55 comprises a motor 83 which is supplied with current from two terminals 56. Secured to the shaft of the motor 35 is a worm 81 (Figure 5) which meshes with a worm wheel 38 which is provided with an extended hub 83. The worm wheel 63 is loosely mounted on a shaft 10 to which is secured an L-shaped member Ii Surrounding the two hubs 69 and 72 is a coil spring I3 one end of which is secured to the hub as and the other end to the hub i2. Two pins 13 and 13 are mounted on the worm wheel 33 and cooperate with the member ii. Secured to the shaft Ill is an arm 11 on the outer end of which is mounted a. roller 18 which rolls on a disc 13 which loosely surrounds the shaft in and which is carried by a bracket 83. The disc i3 is provided with a plurality of notches 3! into which the roller 18 drops when the selector is in its six posltions.

Secured to the upper end of the shaft 10 is a contact arm 32 which consecutively engages the six points of a rotary switch 33. The six of the switch 33 are connected to one side of sin variable condensers B5 of the radio tuner 56. The other sides of the variable condensers are connected to the secondary of a transformer 83 the primary of which is connected to the antenna 31.

Secured to the lower end of the shaft i0 is a contact arm 33 which consecutively engages the six points of a rotary switch it. The six points the frequency converter 01.

of the switch 00 are connected to one side of six variable condensers 0| which form part of the local oscillator circuit 00 which is associated with The output circuit of the frequency converter 01 is connected through a transformer 02 to the input circuit of the intermediate frequency amplifier 00, the output circuit of which is connected through a transformer 00 to the second detector and automatic volume control 00 which is of the twin diode type. The audio and suh-. audio amplifier 0i is of the twin triode type, the plate circuit of the audio-frequency portion being connected to a terminal 00 and the plate cli cuit of the sub-audio frequency portion being connected to a terminal 00. A high voltageter- :minal 01 and a ground terminal 00 are provided.

'output for all of the stations participating.

In Figure 3 are shown the .audio amplifier, loud speaker and scanner motorqamplifler control circuits. These circui tscomprise an audio amplifier I00 provided with two power tubes IOI and I02, a loud speaker I00, a power pack- I00 and a relay control tube I06, which controls the operation of a relay I01. The input circuit of the audio amplifier I00 .is connected to audio frequency terminal 00 and ground terminal 08 of the audio-frequency section of pre-amplifler iii of Fig. 2, the terminals of the input circuit of amplifier I00 being similarly numbered for that reason. The power tubes I0! and I02 are provided with two cathode-toground resistors H0 and III, the former being permanently connected to ground and the latter being connected to ground through armature'100 and back contact I09 of the relay I0'I whenzthe armature is in its normally biased position as shown, due to spring I08. The power pack I00 is supplied from terminals II: with alternating the similarly numbered terminals of Fig. 2,...the

other motor terminal being connected through the switch II3 to one-of. the power supply terminals II2.

The control circuits shown in Figure 4 com- I prise a low pass filter I20, a limiting amplifier I23," a balanced detector I20, a filter amplifier I20, a sub-audible frequency oscillator-I20,

and an amplifier-rectifier I21. The input terminals 00 and 00 of the filter I20; are connected ,to the similarly numbered terminals in Fig. 2 which -constiti'ite the output of the sub-audio. frequency section of preamplifier. 0|. The output terminals III and N0 of amplifier-rectifier I21 are connected to the similarly numbered terminals-z in Fig. 3- which constitute the input to the relay :con-

troltubel00.

The sub-audible frequency oscillator I20 which may be structurally identical with oscillator I0 at the transmitter is so designed that it can produce frequencies ranging from .33 cycles to 01- 'cycles. The frequencies produced by oscillator I20 are controlled a in the case of oscillator I0 by .a plurality of push buttons Iii-I01 which are identified as concert," dance," et cetera and which when depressed cause frequencies of 33, 36,

39, 42, 45, 48 and 51 cycles, respectively, to be produced. It will be noted that the frequency corresponding to any receiver button (concert,

dance, etc.) is 12 cycles-per second greater than .the frequency corresponding to the like-designated transmitter button (concert, dance, etc). The connections above described between the various component parts will be clear from Figure 6 which is a block diagram'of' the over-all receiving system and wherein parts corresponding to like parts in Figures 2 to 5 are denoted by the same reference characters.

Qperation of Figures 2, 3, 4 and 5 In the operation of the-receiver shown in Figures 2-5 when it is desired to receive any particular' type of program, such for example as plays,

the corresponding push button, in this case I00, is depressed andthe switch IIO closed. The depression of the push button I00 causes oscillator I20 to produce a frequency of 42 cycles which will be impressed upon the grids of the balanced detector tube I20.

The closing of the switch III will cause the energization of the relay I0'I as soon as the diaments of the tube I00 have heated up, which will complete a circuit from the A. 0. terminals II2 through the front contact I00 of the relay I01, terminals 0 to the motor 00 which will start rotating. e rotation of the motor 00 causes a slow rotation of the wormwheel 00 and hub 00 I in a counter-clockwise direction as seen in Fig-- pin I0 will engage the member II and will cause the roller to move out of the notch 0|. As soon as this occurs the holding moment of the roller I0 will be reduced and the tensionof the wound up spring II will cause the'member 'II to rotate in a counter-clockwise direction until it engages the pin 10 at which timethe roller I will drop into the next notch 0|.

Iii)

In this way the shaft 10 together with the two contact arms 02 and 00 are caused to move intermittently through a sixth of a revolution so that the contact arms 02 and 00 successively engage the points of the switches 00 and 00 respectively. The contact arms 02 and 00 will remain in engagement with each point of their respective switches 00 and 00.101- a predetermined interval of time which for'example may be six seconds.

During this interval of time each of the six participating transmitting stationawill be tuned in by means. oi the corresponding'condenser 00 and thelocal oscillator circuit 00;.will be tuned by the corresponding condenser 0i to produce the-proper heterodyne frequency for that particular station which will vary from the station frequency bythefrequency of the intermediate circuit 00. The intermediatefrequency modulated by the control frequenoy will then pass through the transformer-02 and will be amplified by the intermediate circuit 00 after which the amplified energy will pass through the trans- 4 assume former l8 and be impressed upon the detector portion of the tube 80 and the grids of the Preamplifier 8|.

The second detector and automatic volume control 80 is of the delayed automatic volume control type in which the cathode bias of the twin triode tube of the preamplifier 8| holds the cathode of the rectifier portion of the twin diode tube 60 positive with respect to ground and the plate of the lower portion of this tube holds the automaticvolume control line substantially at ground potential until the rectifier is actuated by a strong enough signal to make the plate of the lower diode negative with respect to its grounded cathode. That is the automatic volume control action is not operative on weak signals.

The audio and sub-audio frequency signals from the terminal" pass to the similarly numbered terminal of Figure 3 and are amplified by the tube I and the two power tubes IN and I02. The sub-audio signal is relatively weak in relation to the audio signal and much 0! it is filtered out by the filter network between the audio amplifier I00 and the power tubes IM and I02. While the scanner is is operating the relay, Ill is energized and the cathodes of the tubes III and I02 are connected to ground through the resistor IIO. Under these conditions the oathodes o! the tubes "I and I02 have a sufiicient positive bias to prevent the audio frequency tones from the radio tuner operating into the loud speaker I08. In this way the loud speaker I08 remains inoperative while the scanner is is in operation. ,5

The sub-audio and audio frequency signals from the terminal 00 pass to the similarly numbered terminal of Figure 4 and through the low pass filter I20 where thevaudio frequencies are filtered out. The sub-audio frequencies then pass through the limiting amplifier I20 so that they will be impressed on the tube or the balanced detector I24 at the same general level regardless of the station which is under examination. Energy from the sub-audible oscillator I20 is also impressed upon the grids of the tube of the detector I24.

In this case the push button I" is shown as being depressed. so that oscillator energy of 42 cycles is impressed upon the detector I24. The difierence between the sub-audible energy received and that produced by oscillator I20 passes through the filter amplifier I2! which is centered at 12 cycles and is designed to reject sufilciently' fromthetransmittershowninl 'igurelhasa frequency of 30 cycles corresponding to the de-- pression of the push button as for plays the diii'erence between this sub-audible frequency and that produced by oscillator lflwill be 12- cycles. The output energy of 12 cycles from the detector I" will then.pass through the filter amplifier I20 and will be impressed'upon' the amplifier-rectifier I21 producing l near.

well at 8 and .15 cycles. The output of this filter F tive voltage at the terminals III and H8 to decrease the plate current of the relay tube I08 to deenergize the relay I01.

As soon as this occurs the armature I08 oi the relay I0! is caused to move to the right (as viewed in Fig. 3) by action of spring I08 breaking the circuit to the scanner motor 05 which immediately stops, leaving the contact arm 82 in en-- gagement with the proper condenser 85 to tune 10 in the station broadcasting plays." At the same time the armature will engage the back contact I08 of the relay I01 which will bridge the resistor III across the resistor III which gives the power tubes IOI and I02, the proper bias so as to cause them to deliver power to the loud speakfrequency generator I26 is depressed. Energy 0! I 48 cycles will then be impressed upon the grids of the detector I20. This produces a frequency in the plate circuit of 18 cycles with the 30 cycles from the transmitter. This 18 cycle energy does 25 not pass through the filter amplifier I25 so that little or no D. C. voltage will be applied to the grids of the relay tube I08 which will allow sufiicient plate current to flow to energize the relay I01. This will cause the armature I08 to move so to the left thus closing the circuit to the motor I! The scanner 55 will then proceed to scan the various participating stations until it is tuned in to a transmitting station at which the push button l8 for."news has been depressed and which is, therefore, transmitting a sub-audible frequency of 36 cycles. When this 36 cycle energy is received and combined in the detector I24 with the 48 cycle energy produced by the sub-audible frequency oscillator I25 energy of 12 cycles will be produced in the plate circuit of the detector I24. This 12 cycle energy will pass through the filter-amplifier i2! which will cause sufiicient negative voltage to be applied to the grids of the relay tube I06 to deenergize the relay I01. As

50 soon-as this occurs the scanner motor will be stopped and the loud speaker I08 will be made operative, as already "described, to cause the "news" program to be produced by the loud speakerilll. Q

It is thus seen that a system is provided in which any desired type of program may be selected by merely depressing a push button on v the receiver which will cause the selector to become operative and test out each one of the participating stations in succession until the station having the desired program is discovered at which time the selector will be automatically stopped and the loud speaker made operative. In. this way the loud speaker will be maintained silent during the scanning processand will become operative only when the desired type of program has been selected. I

Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited to any specific construction but might be embodied in various forms without departing from the spirit oi the invention or the scope of the appended claims.

What I claim is:

.,. ii Themethod of program selection in radio aseavvs v I broadcasting and the like which comprises assigning a distinctive sub-audible frequency to each particular type of program, as for example, concert, dance music, news, sports, etc. to be transmitted from various stations, transmitting the program and the particular sub-audible frequency corresponding to the type of program to be transmitted from the various stations, and

utilizing the transmitted sub-audible frequency characteristic control frequency, which consists in deriving the control frequency which accompanies that signal-modulated carrier frequency desired to be received, selectively producing at the receiver a second control frequency characteristic of the signal frequency desired to be received, heterodyning the two control frequencies, rectifying the resultant beat frequency, and controlling by means of the rectified current the adjustment of the receiver to the desired signal modulated frequency.

3. The method of automatically adjusting the tuning of a receiver to a desired one of a plurality of signal-modulated carrier frequencies, each of which is accompanied by a sub-audible control frequency, which consists in deriving the control frequency which accompanies that signal-modulated carrier frequency desired to be received, selectively producing at the receiver a second sub-audible control frequency correlated with the control frequency of the signal frequency desired to be received, heterodyning the two control frequencies, rectifying the resultant beat frequency, and controlling by means of the rectified current the tuning of the receiver to the desired signal-modulated frequency. 4. Mechanism for automatically tuning a radio .receiver to a selected one of a plurality of transmitters each carrying a particular type of program which is identified by a simultaneously transmitted characteristic potential receiver control-signal, comprising mechanically driven scanning-means for intermittently and successively tuning said receiver to said plurality of transmitters, selective preset means constructed and arranged for conditioning the receiver so that said potential control-signal can exercise actual control to automatically tune-the receiver to the program corresponding to the operated selective means, and means responsive to said control so constructed and arranged that the scanning means is made inoperative when the receiver is tuned to a transmitter carrying the said particular type of program.

5. Mechanism for automatically tuning a radio receiver according to the invention defined in claim 4; said receiver having a signal indicating device, wherein means are eflective while the scanning means is in operation to cause the signal indicating device of the receiver to be nonresponsive.

6. A system of broadcasttransmission and reception comprising a transmitter provided with means for producing a code signal characteristic of the type of program being broadcast and simultaneously transmitting said code signal and program, the receiver comprising a program channel 'for selecting a desired program, said channel including a tuning device, and means responsive to the characteristic code signal for eifecting adjustment of the tuning device.

'7. A system of broadcast transmission and reception comprising a transmitter provided with 5 means for selectively producing one of a plurality of control signals which is indicative of the type of program being broadcast and simultaneously transmitting said control signal and program, the receiver comprising a program channel and a m control signal channel, said channel including a tuning device, and means included in the latter channel responsive to the control signal for effecting adjustment of the tuning device.

8. In a radio receiver, means for automatically adjusting the tuning of the receiver to a desired one of a plurality of signal-modulated carrier frequencies, each of which is accompanied by a sub-audible. control frequency different from the others, means at the receiver for deriving the A" sub-audible control frequency which accompanies that signal-modulated carrier frequency desired to be received, means for selectively producing at the receiver's second sub-audible control frequency correlated with the derived sub-audible control frequency, means for heterodyning the two control frequencies, means rectifying, the resultant beat frequency, and means under the control of the rectifying means for adjusting the tuning of the receiver to the desired signal frequency.

tive sub-audible frequency to be broadcast by the transmitter during at least a portion of the transmitted program, a receiver including tuning mechanism, means including a device for actuating the tuning mechanism adapted to become 40 operative upon receipt of a sub-audible frequency other than the one that corresponds to the particular class of program desired, and means operative upon receipt of the sub-audible frequency corresponding to the desired classoi' program 5 constructed and arranged to render said tuning mechanism actuating means inoperative and the receiver responsive to a transmitting station broadcasting the desired program.

10. In a broadcast transmission system of the type wherein an auxiliary signal indicative of the class of program is transmitted from the transmitter along with the program modulations on the same radio channel and is utilized at a receiving point to efiect reception by the receiver 5'5 of a particular class of program, a generating device adapted to produce oneof a plurality of different auxiliary signals, means for causing the selective operation of said device atone auxiliary signal, and means for connecting said generating 0 device to the transmitter for impressing theselected auxiliary signal upon the transmitter, whereby the selected auxiliary signal and the program of which it isindicative are simultaineously radiated from the transmitter on the 45 same radio channel.

11. In a broadcast transmission system of the type wherein a sub-audible frequency indicative of the class of program is transmitted from the transmitter and utilized at a receiving point to effect the reception by the receiver of a particular class of program, a vacuum tube generator adapted to produce one of a plurality of sub-audible' frequencies, means for causing the selective operation of the generator at one frequency, and

18 means for connecting said generatorto the trans! .mitter for impressing the selected sub-audible frequency upon the transmitter, whereby the latter frequency and the program of which it is indicative are simultaneously radiated from the transmitter, means at the receiver for deriving the transmitted sub-audible frequency, means at the receiver for producing a sub-audible frequency which is correlated with the derived subaudible frequency, means for combining said two frequencies to derive a control potential, and means for utilizing said control potential to condition the receiver for the reception of the desired class of program.

12. In a broadcasting system, a transmitter adapted to transmit various classes of programs and a receiver adapted to receive such programs, selectively-operable means at the transmitter for producing a sub-audible frequency characteristic of the class of program to be transmitted, the transmitter carrier being modulated by said characteristic frequency and the program, means at the receiver for deriving'the transmitted subaudible frequency, selectively-operable means at the receiver for producing a second sub-audible frequency correlated with the derived sub-audible frequency, and means responsive to the conjoint actiongof said two sub-audible frequencies for ef-' fecting adjusting of the receiver to receive the class of program corresponding to-the operated selective means.

13. In a broadcasting system, a transmitter adapted to transmit various classes of programs and a receiver adapted to receive automatically a selected one of such programs, seiectively-operable means at the transmitter for producing a sub-audible frequency characteristic of the class of program to be transmitted, the transmitter carrier being modulated by said characteristic frequency and the program, means at the receiver for deriving the transmitted sub-audible frequency,selectively-operab1e means at the receiver for producing a second sub-audible frequency correlated with the derived sub-audible frequency, signal translating means adapted to be normally ineffective, and means responsive to the conjoint action of said two sub-audible frequencies for effecting adjustment of the receiver to receive the class of program corresponding to the operated selective means and to cause the signal translating means to become effective.

14. A radio receiver comprising tuning means 'for adiusting the receiver for the reception of predetermined signal-modulated carrier frequencies, each of said carrier frequencies having superimposed thereon a predetermined identifying sub-audible control frequency supplied by the transmitter, means at the receiver, for deriving the identifying sub-audible frequency from the selected signal-modulated carrier frequency, a motor for actuating 'the tuning means, a plurality of selectors each corresponding to one of the predetermined carrier frequencies to be received, means under the control of each selector for producing a distinctive sub-audible frequency, the identifying sub-audible control frequency accompanying the received carrier frequency having a definite relation to the sub-audible frequency produced by the selector corresponding to said carrier frequency, means for heterodyning said two sub-audible frequencies, means for deriving a voltage proportional to the resultant beat frequency, and control means for the motor adapted to maintain the 'motor energized and to actuate the tuning means so long as the derived voltage results from the combination of two sub-audible aeeeme" frequencies which do not have a predetermined definite relation, said control adapted, when the derived voltage results from the combination of two sub-audible frequencies which have a predetermined definite relation, to adjust the tuning means to a predetermined carrier frequency position and to deenergize the motor.

15. A radio receiver comprising tuning means for adjusting the receiver for the reception of predetermined signal-modulated carrier frequencies, each of said carrier frequencies having superimposed thereon a predetermined identifying sub-audible control frequency supplied by the transmitter, meansat the receiver for deriving the identifying sub-audible frequency from the selected signal-modulated carrier frequency, a motor for actuating the .tuning means, a plurality of selectors each corresponding to one of the predetermined carrier frequencies to be received, means under the control of each selector for producing a distinctive sub-audible frequency, the identifying sub-audible control frequency accompanying the received carrier frequency having a definite relation to the sub-audible frequency produced by the selector corresponding to said carrier frequency, a branch'circuit comprising means whereby the carrier frequencies are derived and reproduced, a second branch circuit comprising means whereby the control frequency is derived and mixed with the frequency produced by the selector, means for deriving a voltage corresponding to the combined frequencies, and control means'for the motor adapted to maintain the motor energized and thus actuating the tuning means so long as the derived voltage results from the combination of two sub-audible frequencies which do not have a predetermined deflnite relation, said control means being adapted, when the derived voltage results from the combination of two sub-audible frequencies which have a predetermined definite relation, to adjust the tuning means to a predetermined carrier frequency position and to deenergize the motor;

16. A radio receiver for automatically selecting a carrier wave which is signal modulated by. a desired type of program and control-modulated by a sub-audible frequency identifying and accompanying the desired type of program, comprising means for tuning to and receiving the energy of a carrier wave, means for producing signal energy and sub-audible control energy corresponding to modulation of said received energy, local sub-audible frequency oscillator, means solectively preset to produce energy of a frequency differing from the control frequency corresponding to the desired type of program by a fixed frequency value, a control circuit responsive to energy only of said fixed frequency value. heterodyne means for producing energy of a frequency equal to the difference of the locally produced sub-audible frequency and the sub-audible frequency derived from the modulations of the received carrier wave, to which the receiver is tuned, means for impressing said difference frequency energy upon said control circuit, and means under control of said control circuit for causing the receiver to select another carrier wave unless the said difference frequency is equal means being e v v mascara 4 prising meens for timing top-mi receiving the en; ergy of a carrier wave. means for producing signal energy and sub-audible control energy. corresponding to modulation of said received energy; local sub-audible frequency oscillator means 015- a. fixed n-ecslly produced sub-audible frequency and. the

. sub-audible frequency derived from the module.- tionsof the received carrier wave, to which the receiver'is tuned, means for impressing said difference frequency energy upon said fixed charact'eristic relay-operating control circuit, and

means causing the receiver to select-another carrier wave unless theesaid diflerence frequency a equal to said fixed frequency value. k

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